Dual frequency induction heating apparatus



R. S. SEGSWORTH DUAL FREQUENCY INDUCTION HEATING APPARATUS Feb. 16, 1954 3 Sheets-Sheet 1 Filed June 15, 1952 4mm ROBERT 5. szaswolem t \f a M5 xwmkmm QEQQ r a 0 00m \N Feb. 16, 1954 R. s. SEGSWORTH DUAL FREQUENCY INDUCTION HEATING APPARATUS Filed June 13, 1952 3 Sheets-Sheet 2 N mw Feb. 16, 1954 5, s swo I 2,669,647

DUAL FREQUENCY INDUCTION HEATING APPARATUS Filed. June 15, 1952 5 Sheets-Sheet 5 ROBERT 5 .SEGSWORT/l Patented Feb. 16, 1954 DUAL FREQUENCY INDUCTION HEATING APPARATUS Robert Sidney Segsworth, Toronto, Ontario, Canada, assignor to The General Engineering Com- D y Canada (Canada) Limited, Toronto, Ontario,

Application June'13, 1952, Serial No. 293,274

8 Claims.

This invention relates to combined low-frequency high-frequency induction heating apparatus.

.This application is co-pending with applications filed on even date herewith: Dual Frequency Induction Heating Method, Serial No. 293,273; Method and Apparatus for Heating Stacked Plates, Serial No. 298,275; Induction Heating Coil Construction, Serial No. 293,276.

Accordingly, hollow shells and like irregularly shaped articles are usually heated in gas fired furnaces and the like. Any attem t to inductively heat such articles by prior methods and apparatus is limited by the non-uniform generation of heat inthe article having regard to the characteristic of the effect of frequency on the depth of. penetration of the magnetic flux.

The induction apparatus of the in ention avoids the disadvantages of non-uniform heating effect on the article and is. accordingly, adaptable to the heating of hollow shells and other irregularly shaped articles.

The apparatus of the invention generally comprises low and high frequency induction heating coils combined and arranged in such manner that the article to be heated is first passed through the low frequency coils to cause the article or a part thereof to be heated to a predetermined temperature and then passed through a higher frequency coil or coils to increase the heating effect on or selectively heat other portions of the article. Means are provided for feeding the article on a through path extending through the influence of the magnetic fields of the low and high frequency coils. Preferably, the article is passed along the co-axial line of the coils, the latter being arranged end to end. Means are provided for guiding the article after discharge from the high frequency coil to a supporting means associated with means for controllably cooling the article. The apparatus may also inelude a further low frequency coil or coils through which the cooled article may be fed for further heat treating.

The invention will be appreciated in more detail by a study of the following specification taken in conjunction with the accompanying drawings.

In the drawings:

,Figure 1 is an electrical schematic of induction heat treating apparatus according to the invention.

Figure 2 is a plan vi w of one form of heat treating apparatus according to thej'invention.

Figur 3 i a sect o al V ew of. t ea t s o Figure} ..illustrating the mechanical features (Cl. BIB-10.71)

A combined low-frequency high-frequency induction heating system is provided in accordance with the invention in a manner illustrated in Figure 1 wherein the high frequency induction heating coil I0 is placed on an axial line with low frequency induction heating coils H, l2 and I3, the arrangement being adapted for the passage of a metal object (not shown) in the direction of the arrow Y.

The high frequency induction heating coil I0 is in parallel circuit with the high frequency capacitor M and switching means 15 to be energized by a suitable high frequency generator It, the latter being driven by a suitable motor l1. Other equivalent sources of high frequency power known to skilled persons may be employed without departng from the concept herein of cooperating low and high frequency induction heating systems. In the illustration disclosed, three phase power is fed from industrial power lines to the terminals 18, I9 and 28 which are electrically connected to the motor through a suitable switch device 2!. These terminals also are connected electrically through theswitching device 22 to the low frequency coils ll, [2 and I3 in a special way.

Observe that the centre coil [2 is connected in reversed manner as one provides the connection of a medial winding in a three phase squirrel cage motor. Low frequency capacitors 23, 24 and 25 are provided, the lectrical arrangement illustrated being in delta connection, it being understood that a star connection of three phase power may also be employed.

It is intended that the low frequency coils ll, I2 and [3 will operate at line frequency of about sixty cycles per second. In the commercial heating of steel with the apparatus of the invention, it has been shown that in excess of of the electrical energy as supplied to the low frequency coils can be converted into useful heat in the metal object being heated up to a temperature approaching the Curie point.

A preferred form of apparatus for heating a hollow shell is illustrated in Figures 2 and 3. An inclined hopper 26 is disposed transversely of the axial line 2l' of the heat treating apparatus 28. A plura ity of shell casings may be arranged in sideby-side relationship in the hopper 26, the lowermost resting in the breach 29 of the feed apparatus i30, the'latter including an axially disposed ram 3|v actuable hythe air cylinder 32 supported by brackets 33 on the rigid longitudinally disposed'concrete panel-314 "supported by frame 35. Uponactuation of the air cylinder underair presa seri s of three all supported by a common frame 3 and having a continuous steel liner 38 therethrough disposed about said axial line 2'1. The low freq ency coils 36, 32 and d are preferably of a construction disclosed in my co-pending application, Induction Heating Coil Construction, Serial No. 293,276, previously referred to. In the apparatus illustrated, each coil may comprise six layers of diameter copper tubing of 52 turns per layer wound over two layers of asbestos coth separating the innermost winding from the liner 3%. The voltage is adjusted to suit the heating rate desired and has a maximum value of about 575 volts at 60 cycles. In accordance with the schematic of Figure 1, the coils may be energized by a three phase source. The windings must be insulated preferably with a resin bonded glass tape with an asbestos paper between layers. The coil must be mechanically sound against the effects of vibration and, accordingy, the windings and insulation must be well bonded with a suitable resin and baked. In some applications it may be desirable to proportion the windings between the low frequency coils to balance the load on the three phase line because it will be apparent that the last coil 40, for example. will be operating on a material which, because of its higher temperature, is different in electromagnetic properties from the material at a lower temperature in, say, coil 36.

The higher frequency coils ii and 42 may be constructed in accordance with conventional practice. In one particular case, however, it was found that a frequency of 360 cycles was an optimum for the desired heat pattern on a three inch diameter shell and, accordingy, multi-layer coils were formed in a manner following the construction of the low frequency coils and comprised in coil ti, four layers at 52 turns per layer of 4" diameter copper tubing: in coil 42. five layers at 37 turns per layer of diameter copper tubing. In this special construction, the high frequency cois were connected in parallel on a single phase line of 400 volts, 360 cycles.

The coil M and the liner 43 are supported rigidly in the frame 37. The coil 42 and liner 44 are disposed upon a swingable mounting 45 pivoted as at it on a bracket 41 fixed to the panel 32. Accordingly, as an article such as a shell arrives at final temperature in the coil 42, the latter may be swung counterclockwise by means of a crank arm 50, actuated by air cylinder A61) to cause the casing to fall through the guide 48, the latter carrying the arcuately formed guide plate 49 against which the outward projectab e end of the casing within the coil 42 may slide as the coil rotates downwardly to the vertical position.

The casing then falls through the guide it into suitable apparatus for controlling the cooling thereof, such as a quenching tank 56] wherein supporting means are provided and which may include a swingab e post 52 over which the casing may rest during the quenching operation.

After the casing has been quenched or controllably cooled, such as in the quenching tank 50, for a desired period of time, the swingable post and its base 53 pivoted on the axle 5A in brackets 55 is swung counterclockwise in the direction of the arrow Y by movement of the arm 55 fastened to the base and actuated by the linkage 5'i operated by the air cylinder 58 to cause the casing 59 to lie in the guideway 60.

A swingable feed arm 6! pivoted as at 62 in brackets 63 is drawn by the arm pivoted as at 65 under action of the inclined air cylinder 65 to cause the bifurcated arms 51 thereof to ride about the post 52 and to engage the shell 59 and move it upwardly to a position indicated in chain lines at 08 supportable by the spring-biased deflectable locking arm 69 mounted on brackets Hi. The casings then pass progressively under action of this feeding apparatus through the stainless steel tube ll about which I preferably form a seies of low frequency coils 12 similar in all respects to the low frequency coils 36, 39 and 40. As indicated, a conveying tube 13 may extend upwardly from the inclined low frequency coils 2 to a pointof deliver (not shown), it being understood, however, that if desired the shell may be cooled in any controlled manner either whi e passing through the tube 13 or after delivery therefrom. The various air cylinders 32, 16b, 53 and 05 may be independently operated by suitable controls of well known character to skilled persons or may be operatively inter-related to provide a substantially automatic system by any of the well known schemes for sequential operation of hydraulic cylinders. It will be appreciated that all of the air cylinders, which of course may be hydraulic cylinders if desired, are of the double-acting type.

A suitable frame M is provided for supporting the groups of necessary capacitors 15 required in accordance with the electrical schematic of Figure 1.

As illustrated in Figure 1, I may provide a temperature indicating device such as an ammeter Ma placed in series with a high frequency coil ill. The ammeter may be shunted in accordance with known practice and may be calibrated to indicate the temperature as a function of current. In this way a very accurate temperature indication can be obtained.

The following table lists the frequency size relationship for optimum efficiency of various materials heated at various frequencies. Reasonable results can be obtained with sizes smaller than those indicated down to about of the minimum sizes listed.

Table Minimum size, inches, for optimum frequency Frequency Material Die. Tube wall round square Thickness Steel Below Curie 2% 1% Point. Steel Above Curie 7 if 3% Point. Aluminum 2% 2 1 3% 2% 1240 525 375 187 68 48 24 89 63 31 312 22 11 Point. Steel Above Curie 1% 1%; l

Point. Aluminum 405 29 Brass 526 372 186 9,6 Steel Below Curie .174 123 062 Poin Steel Above Curie .83 585 292 Point. Aluminum 226 l6 08 Brass r .284 .20 .10 Steel Below Curie 029 021 01 Point. Stecl Above Curie 12S 091 I .045

Point. 400,000 Aluminum 035 O25 012 400,000 Brass .045 032 016 The particular relation between frequency,

May, Chapman and Hall, pages 167 and 169).

in 12W PG V where A==depth (in cms.) to accommodate the total magnetic flux if it were uniformly distributed atthe same density as exists at the surface. r=resistivity of the charge, in electromagnetic units (resistivity of a 1 cm. cube in ohms) 10 =r 10 W 21r frequency in cycles per second. f=frequency. Pe efiective permeability of the chargezratio of It will be apparent that the particular frequency for a predetermined desired depth of penetration is related to and is a function of the efiective permeability of the material and the resistivity.

In the heating of specially shaped objects such as hollow shells, a particular heat pattern may be desired in the shell base rather than a uniform heat pattern. In such instance, the high frequency induction heating part of the apparatus may operate at a higher frequency giving lesser penetration. In the case where one is heat treating a shell, the shell wall determines the desired depth of penetration and, accordingly, a higher frequency may be employed of the order of ten thousand cycles per second. If a frequency of materially greater penetration were employed there would be a subtantial overlap of heating ailects in the base of the shell outside a centre region thereof. Accordingly, the centre region can be heated to a diiferent degree than the outer regions not only by selecting the frequency of the high frequency induction heating coils but by controlling the duration of heating in the low frequency induc-- tion coils. In this way, a controllable heat pattern can be accomplished wherein the outer skin is always heated to the same or a greater temperature than the core of the material in a solid metal object. ticularly to the heat treatment of various shaped castings wherein the heat pattern of the heat treating can be controlled in a specified way before quenching or controlled cooling by any other well known technique in the tempering and hardening arts.

It Will be apparent that the present multiple frequency induction heating apparatus, in af-- fording a control over the heat pattern, enables a substantially uniform heating of an article to be accomplished by an induction heating technique.

It is intended that the present disclosure should not be construed in any limiting sense other than that indicated by the scope of the following claims.

What I claim as my invention is:

1. Apparatus for heat treating a shell case comprising in combination: a stationary horizontally disposed induction heating coil including means for energizing same; means for passing a shell case through said coil; a swingable induction heating coil having an exit end and supported in coaxial alignment with said stationary coil; means swingably supporting said The technique lends itself parswinga'bl'e coil for swinging movement between" said coaxial position and a downward substantially vertical position thereof; cooling means I disposed below said swingable coil including a support; and means for guiding a shell case to said support as said case falls from the exit end of said swingable coil upon moving the latter to substantially the vertical position.

2. Apparatus as claimed in claim 1 in which said guide means is in the form of a curved plate spacedadjacent the path of movement of the exit end of said swingable coil during swinging movement thereof.

3. Apparatus as claimed in claim 1 and an inclinedguideway rising from adjacent said support to a point exterior of said cooling means; means swinging said support and a shell case thereon to a position substantially placing said shell case on said inclined guideway; and means for moving said placed shell case from said support and along said inclined guideway exterior of said cooling means.

4. Apparatus as claimed in claim 1 and an inclined guideway rising from adjacent said support to a point exterior of said cooling means; means swinging said support and a shell case thereon to a position substantially placing said shell case on said inclined guideway; means for moving said placed shell case from said support and along said inclined guideway exterior of said cooling means; means for supporting said shell case on said guideway exterior of said cooling means; and a further induction heating coil including energizing means therefor disposed coaxially with said inclined guideway and forming a continuation thereof beyond said cooling means.

5. Apparatus as claimed in claim 1 and an inclined guideway rising from adjacent said support to a point exterior of said cooling means; means swinging said support and a shell case thereon to a position substantially placing said shell case on said inclined guideway; a swingable arm disposed in said cooling means having bifurcated arms on the free end thereof adapted upon swinging movement of said arm to engage and move said placed shell case from said support and upwardly along said inclined guideway to a position exterior of said cooling means.

6. Apparatus as claimed in claim 1 in which said guide means is in the form of a curved plate spaced adjacent the path of movement of the exit end of said swingable coil during swinging movement thereof; an inclined guideway rising from adjacent said support to a point exterior of said cooling means; means swinging said support and a shell case thereon to a position substantially placing said shell case on said inclined guideway; and means for moving said placed shell case from said support and along said inclined guideway exterior of said cooling means.

'7. Apparatus as claimed in claim 1 in which said guide means is in the form of a curved plate spaced adjacent the path of movement of the exit end of said swingable coil during swinging movement thereof; and inclined guideway rising from ad acent said support to a point exterior of said cooling means; means swinging said support and a shell case thereon to a position substantially placing said shell case on said inclined guideway; means for moving said placed shell case from said support and along said inclined guideway exterior of said cooling means; means for supporting said shell case on said guideway exterior of said cooling means; and a further induction heating coil including energizing means therefor disposed coaxially with said inclined guideway and forming a continuation thereof beyond said cooling means.

8. Apparatus as claimed in claim 1 in which said guide means is in the form of a curved plate spaced adjacent the path of movement of the exit end of said swingable coil during swinging movement thereof; an inclined guideway rising from adjacent said support to a point exterior of said cooling means; means swinging said support and a shell case thereon to a position substantially placing said shell case on said inclined guideway; a swingable arm disposed in said cooling means having bifurcated arms on the free end thereof adapted upon swinging movement of said arm to engage and move said placed shell case from said support and upwardly along said inclined guideway to a position exterior of said cooling means.

ROBERT SIDNEY SEGSWORTH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,646,498 Seede Oct. 25, 1927 1,900,842 Northrup Mar. 7, 1933 1,980,875 Northrup Nov. 13, 1934: 2,202,758 Denneen et a1. May 28, 1940 2,281,334 Somes Apr. 28, 1942 2,322,777 Purnell June 29, 1943 2,604,577 Strickland, Jr. et a1. July 22, 1952 

